Compliant suspension cable

ABSTRACT

Compliant, nonstrumming, high strength composite cable for sonobuoy suspension system. Nonabsorbent relatively inelastic strands of textile yarn are bound onto an elastomeric warp strand by two counterwound helixes of textile stretch yarn. The inelastic yarn forms random transverse loops along the cable by protruding outwardly through the openings between the helical windings.

United States Patent 1 3,696,325 Tallman 51 Oct. 3, 1972 [5 CONIPLIANT SUSPENSION CABLE Primary Examiner-Richard A. Farley Inventor: Charles V. Tallnun, Rye Beach,

The United States of America as represented by the Secretary of the Navy Filed: May 14, 1970 Appl. No.: 37,074

Assignee:

US. Cl ..340/2, 9/8 R, 340/8 S Int. Cl. ..I'I04b 11/00, B63b 21/52 Field of Search ..340/2, 3 T, 8 S; 9/8 R References Cited UNITED STATES PATENTS 11/1970 Dale et a1. ..340/2 Attomey-R. S. Sciascia and Henry Hansen [57] ABSTRACT Compliant, nonstrumming, high strength composite cable for sonobuoy suspension system. Nonabsorbent relatively inelastic strands of textile yarn are bound onto an elastomeric warp strand by two counterwound helixes of textile stretch yarn. The inelastic yarn forms random transverse loops along the cable by protruding outwardly through the openings between the helical windings.

l Cla1m, 3 Drawing Figures PATENTEUIIBI 3 m2 INVENTOR.

CHARLES V. TALLMAN 2; M

LOAD

ATTORNEY 1 COMPLIANT SUSPENSION CABLE STATEMENT OF GOVERNMENT INTEREST BACKGROUND OF THE INVENTION The invention relates in general to composite suspension cables and more particularly to new and improved composite elastic cables for underwater use having antistrumming fringe and at least one relatively inelastic longitudinal strand and to methods of making such cables.

Underwater listening or sonar systems often employ remote sonobuoy stations having hydrophones or transducers suspended from a buoyant float containing transmitter or receiver. Suspension cables for the transducers are commonly made of compliant or elastic material to maintain the transducer at a fixed vertical level regardless of the frequently erratic movement imparted to the float by wave action on the surface. In addition, transverse ocean currents relative to a sub merged vertical cable induce natural vibration or strumming of the cable causing vertical oscillation of the load. Compliance enhances the strumming effect, and if the load is a sensitive hydrophone, the spurious noise thus contributed to the background level may obscure a target signal.

One type of prior art antistrumming cable is shown in an application entitled Improved Hydrophone Suspension Cable" by Charles V. Tallman, Ser. No. 803,763, filed Mar. 3, I969. The larger, woven cable, while ideal for use with relatively heavy loads, did not address itself to the special problems encountered with very light loads of a few ounces. Loads on this order are achieved even with massive transducer assemblies by incorporating buoyant material to reduce their weight in water. The load reduction, however, demands a similar decrease in the size and spring constant of the cable. On the other hand, towing of the sonobuoy or extremely rough sea may place abnormally high, transient stress on the cable. Thus, the suspension cable must be reliably operable over a wide range of tension, from a few ounces to several pounds or more.

All of the prior art cables which provide antistrumming fringe have numerous woven or braided elements requiring expensive machinery for fabrication. Usually the limit or break strength is determined solely by the strength of the compliant core. As a result, many of the prior art cables cannot be scaled down to yield the desired compliance for light loads without lowering their break strength below acceptable levels.

SUMMARY OF THE INVENTION Accordingly one of the principal objects of the invention is to provide a compliant, high-strength suspension cable for suppressing noise generated by strumming. Another object of the invention is to provide a nonwoven elastic suspension cable of low spring constant which may be easily manufactured. A further object is to increase the ratio of break strength to design load in a compliant suspension cable.

2 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation view of a sonobuoy deployed in water with a suspension cable constructed according to the invention;

FIG. 2 is an enlarged view of the cable of FIG. 1; and

FIG. 3 is an enlarged view of the cable of FIG. 1 fully stretched.

DESCRIPTION OF THE PREFERRED EMBODIMENT A sonobuoy is shown in FIG. 1 having a piezoelectric transducer assembly 10 suspended by a compliant cable 11 from a buoyant cylindrical float 12 which carries an amplifier and RF. transmitter (not shown) and a whip antenna 13. lfthe sonobuoy is active rather than passive, that is, noise is to be generated rather than received by transducer 10, the transmitter will be replaced by an RF. receiver enabling remote control of the transducer output. Electrical connection between float 12 and transducer 10 is provided by wire 14 which forms an open, loosely-wound helix surrounding cable 11. The diameter of the helix greatly exceeds that of cable 11 to prevent interference. The sea water itself may be used for the grounded side of the electrical circuit.

The improved suspension cable 11 shown in more detail in FIG. 2 includes a relatively inelastic strand bundle 16 bound to an elastic warp element 17 by means of mesh-forming cover threads 18 and 19 which are wrapped on the cable in counterwound helixes having non-uniform pitch. In the larger open areas between cover threads 18 and 19, inelastic strands l6 protrude laterally to form intermittent loops 21. Between loops 21 threads 18 and 19 pass over the strand bundle 16 securing it to the elastic warp element. Due to the non-uniform helical pitch in threads 18 and 19, the loops occur at random intervals and serve as antistrumming fringe for noise suppression.

Warp element 17 is made from an elastic material such as a high-stretch, highly resilient synthetic rubber. Preferably, the warp material should be extensible to at least six times its unstretched length without exceeding its elastic limit. A preferred material for the warp element is 20 gauge, isoprenepolybutadiene blend synthetic rubber having a square cross section. The spring constant may be varied as desired for different loads by increasing the gauge or cross-sectional area of the elastic warp element or by using a plurality of such elements. Other synthetic rubbers, elastomers and elastic materials can be used depending on the stressstrain and frequency levels sought.

Multiple strands 16 which form the loops 21 are made of a nonabsorbent textile yarn such as 840 denier o-tum twist polypropylene or polyester. The stress of the design load will be carried exclusively by elastic warp element 17. However at full extension, multiple strands 16 will be taut and loops 21 will no longer be present. At this point substantially all of the load will be borne by strands 16 which are made of relatively inelastic fibers. The number and denier of strands 16 may be varied depending on the loop density and strength desired. Six strands have been found suitable for a 4 ounce load. The break strength of the composite cable is determined by the summated strength of the strands l6.

The helically wound cover threads 18 and 19 are preferably made of textile stretch yarn. Any overload on the cable will thus be borne entirely by the stronger inelastic yarns in the strand bundle 16. A yarn found suitable for this purpose is 70 denier Helanca nylon which reaches its limit of stretch at about 50 percent. However other low denier elastic fibers may be substituted for the cover threads.

One method of making the suspension cable 11 of F IG. 2 is to prestretch elastic warp element 17 and bind the straight strand bundle l6 thereto by wrapping cover threads 18 and 19 in counterwound helixes of uniform pitch as shown in FIG. 3. When the tension is released, strand bundle l6 pushes through'the openings between cover threads 18 and 19 at random intervals to form loops 21 in cable 11, illustrated in FIG. 2 under normal load conditions. As the elastomer l7 contracts, slack is introduced into strand bundle 16. The original uniform winding pattern is distorted as threads 18 and 19 are forced apart at various points along the length of the cable. The number of turns between any two resulting loops 21 may vary from I to or more depending on the bunching or decreased pitch between loops 21 caused by the spreading of threads 18 and 19. The exact spacing between any two loops is noncritical. The original pitch on the wrapping helixes is also noncritical and may be adjusted to give the composite texture sought. Typically, the cable might have 80 turns per foot when fully stretched.

Alternatively, cover threads 18 and 19 may be wound initially in helixes having a regularly varying pitch. in this way, the position of loops 21 after relaxation may be predetermined, if desired.

In manufacture, the stretched element 17 and strand bundle 16 are juxtaposed and passed concurrently up through two counterrotating spindles. As the elements pass through each spindle, a helix of textile stretch yarns l8 and 19 is wound around the bundle of strands l6 and the elastic warp element 17. Tension on wrapping yarns 18 and 19 is regulated by flier or ring traveler constraints. Since the pitch of each helix is to remain uniform, the elements to be wrapped are fed through the spindle area at constant speed. The spindle rotation speeds also remain constant. Statecf-the-art rubber covering machines encompass the needed speed ratios and spindle bores determined with reference to the denier of the wrapping threads 18 and 19 and the desired pitch or number of turns per inch thereof. The initial tension on the elastic warp element 17 may range approximately from 200 to 600 percent. The higher the initial stretch, the coarser side loops 21 will be. A suitable initial stretch has been determined to be about 380 percent,

An important advantage of the invention is the elimination of the complex machinery formerly necessary to form and maintain side loops or fringe on the suspension cable. In the manufacturing stage of the cable, no loops are present to interfere with the assembling of the constituent elements of the cable. The final stage of manufacture is automatically completed by releasing tension on the cable. The self-deploying loops 2] automatically distribute themselves in random fashion selecting appropriate areas for protrusion and spreading of cover threads 18 and 19. Moreover, manufacture does not require weaving on a fabric loom and can be conveniently performed on conventional f' li ga i ameters of the improved cable 11 may be varied according to specific design criteria in a manner familiar to those skilled in the art. The spring constant of a given embodiment of the cable according to the invention is not strictly constant over its elastic range and increases as increased tension causes the cable's length to approach the limit of elongation. As a result, compliance may be reduced below the acceptable level. Thus, for heavier loads the diameter of the cable may have to be increased. The amount of tension produced under water by a given mass may be reduced by providing a determined amount of buoyancy within the load.

If the sonobuoy employs a passive hydrophone responsive to a selected bandwidth, the dimensions of the cable can be adjusted to obtain a natural, undamped strumming frequency outside of the selected bandwith. Antistrumming loops 21 will still be needed, however, since some of the harmonics and associated frequencies may lie within the bandwidth.

There are many different means for the electrical connection between transducer 10 and float 12. For example, instead of a loose helix, wire 14 may form a se ries of open loops attached at relatively long intervals to cable 11. Alternatively, electrically conductive fibers may be used in strand bundle 16. If the diameter of the warp element 11 permits, wire 14 may be slidably carried within a central bore in element 17. However, some means of eliminating slack in the wire would be necessary, such ,as a tension-maintaining spool located in float l2.

Besides manufacturing convenience, the invention provides a new cable having an increased breakstrength-to-load ratio, typically about I40, far in excess of that achieved by prior art compliant cables. The combination of an antistrumming fringe or loope network with high break strength in a miniature elastic cable is believed to be unprecedented. The new cable also meets the critical size and weight limitations dictated by available storage space and pay out mechanisms, especially where transducer depths of several hundred feet are desired.

It will be understood that various changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In a sonobuoy having a buoyant float; a transducer suspended by a compliant member from the float; and a receiver/transmitter unit carried by the float, said unit operatively connected with said transducer for controlling and transmitting the output of said transducer; wherein the improvement comprises:

a strand adjacent to said compliant member and extending along the length of said member with intermittently protruding loops; and

a mesh binding said strand between adjacent loops to said member, said mesh comprising a plurality of counterwound thread elements operatively engaging and surrounding said strand and said member, said thread elements being counterwound in helical configurations of non-uniform pitch,

Q: s v t 

1. In a sonobuoy having a buoyant float; a transducer suspended by a compliant member from the float; and a receiver/transmitter unit carried by the float, said unit operatively connected with said transducer for controlling and transmitting the output of said transducer; wherein the improvement comprises: a strand adjacent to said compliant member and extending along the length of said member with intermittently protruding loops; and a mesh binding said strand between adjacent loops to said member, said mesh comprising a plurality of counterwound thread elements operatively engaging and surrounding said strand and said member, said thread elements being counterwound in helical configurations of non-uniform pitch. 